Motor-fan assemblies are well known for generation of a directed airflow. Applications using a directed airflow include, but are not limited to, material handling/drying, air sampling, cooling applications, ink drying, and cleaning systems.
FIG. 1 shows a Prior Art motor-fan assembly designated generally by the numeral 50. The assembly 50 includes a motor enclosure 52 with a motor section 54 connected to a fan section 56. A working air inlet 58 axially extends from the fan section 56 which carries a working fan assembly designated generally by the numeral 60. Air is drawn in through the inlet 58 and expelled out a tangential working air outlet 62. A motor blower bracket 64 connects the sections 54 and 56 to one another while keeping the working air isolated from the motor section. The motor section 54 includes a circuit board 66 which is supported by the motor blower bracket 64. Coupled to the circuit board 66 is a brushless motor 68 which includes a stator 70 and a rotor 72 which carries magnets in a manner well known in the art and wherein the rotor has extending therefrom a shaft 74 which extends through the motor blower bracket 64 and rotates the rotatable fans included in the working fan assembly 60. Also connected to the shaft 74 is a cooling fan 76 maintained in the motor section 54. The motor section 54 provides an axial cooling fan inlet 80 and a cooling fan outlet 82 which is typically radially directed from the motor section 54. Rotation of the cooling fan draws air into the motor section 54 through the inlet 80 for the purpose of cooling the stator 70, its associated windings, and the circuit board 66. The cooling airflow then exits through the outlet 82.
Although the Prior Art motor-fan assembly 50 is effective, it experiences performance issues that are fairly well known. The first significant issue is that the power output, especially in brushless-type configurations, is constrained by the positioning of the motor assembly and driving electronics within the motor section 54. The stator windings and certain circuit components, namely a power module and a diode bridge, generate significant amounts of heat. If not adequately cooled, the associated electronics stop performing, which results in a thermal shutdown of the motor 68. Operation of the cooling fan minimizes this from occurring, but overheating reduces operational performance of the motor assembly. It will also be appreciated that the heat, over time, decreases motor life.
The second significant performance issue is related to the generation of noise. The cooling fan flows air over the electronics, but the fan and inlet vents provide sharp edges which generate noise and most vents are axially disposed in relation to the cooling fan so that the noise permeates outwardly with little to no impediment. Filters and mufflers may be provided, but at an added cost and overall motor size increase. Additionally, the vents do little to prevent contaminants from entering the cooling air intake, especially when the motor is in an off condition.
Other drawbacks of current motor configurations are that the inlet and outlet vents are not easily adapted to modification. For example, if the cooling air is maintained in a dirty environment then filters are required, but the filters reduce the cooling airflow, which may lead to overheating. Special fixtures may also need to be mounted to the airflow inlets and outlets for the cooling air, but these are cumbersome and require construction of unique motor sections. Another drawback is that there are typically issues with contaminants from the cooling airflow entering into the working airflow. Finally, current motor-fan assemblies are not well suited for preventing heat migration from the working fan assembly via the motor shaft to the motor section.
Accordingly, there is a need in the art for a motor-fan assembly which isolates a bearing from heat generated by a working fan assembly. In particular, there is a need in the art for a motor-fan assembly that interposes a blower housing between the bearing and the working fan assembly so as to minimize heat migration from the working fan assembly into the bearing, thus improving bearing life.